The present invention relates to an improved device for precision measurement of magnitudes and a method to verify the correct functioning of the device.
Devices for accurate measurements of magnitudes, such as measurements of pressure and force, have been available on the market for some time.
Such devices are better known as transducers and are essentially composed of electrical circuitry, configured as a Wheatstone bridge, in which the circuit resistors, usually known as extensometers, are fixed, usually glued, to a laminar base, usually made of steel, which is deformable, according to an elastic constant.
Because of this characteristic, every time a deformation of the base occurs, due to load stress, a proportional variation of the absolute value of one or more resistors and the measurement of such differential value, caused by the modification, when correctly interpolated, gives the measurement of the value required.
However, such known transducers are subjected to faults and malfunctioning which affect their precision, hence their reliability.
Faults in the manufacturing process or accidental collisions or knocking of the devices can cause a progressive detachment of one of the resistors, or the partial detachment of the base, which in turn will cause the modification of its absolute value, with subsequent wrong reading of the measured magnitude.
However, if it is of a macroscopic order, the wrong reading can be easily detected because in activating the transducer in discharge configuration, it must display the reference value set by the manufacturer. This value, starting from the "zero" origin value, takes into account the sensitivity set by the manufacturer of all the elements of which the transducer is made and, as stated above, if the difference between the expected value and the value effectively found is excessive, it means that the transducer is damaged beyond repair and must be replaced.
On the other hand, if the reference value is verified before the start-up of the transducer, this does not necessarily mean that the transducer is intact and reliable.
The anomaly can appear after the installation of the transducer, and, therefore, the anomaly cannot be detected.
In this latter case, it can be quite dangerous in those circumstances in which the transducer is used in machines in a medical environment. For example, when the transducer is an integral part of a machine that automatically controls volumes of liquid medicinals to be infused or exchanged in a patient.
More precisely, for therapies such as dialysis, these transducers are used to weigh bags containing medicinal solutions that are to be progressively infused into the patient over a predetermined period of time with a predetermined and precise volume of these solutions, vis-a-vis of a similarly programmed subtraction of fluids drained from the patient.
A malfunction of the transducer that occurs during the treatment can put the patient in severe danger, because the actual administration or the subtraction of solution will have different values from those originally programmed. As a result, the originally programmed administration or subtraction can run out-of-control and not be detected until the end of the treatment, after the patient has already suffered physical damage.
Current attempts to eliminate such problems and to avoid the risk related to them include, for example, procedures to verify the correct functionality of the electronics by modifying, at programed intervals, the transducer's signal output. However, this verification does not provide information on the state of structural wear and tear of the transducer internal circuitry.
Thus, a transducer malfunction could be interpreted as an incorrect application of the therapeutic treatment, and it would be corrected automatically, paradoxically worsening the patient's condition.
The second method of verification of correct functioning of the device involves coupling two transducers, which control each other, and intervene in case of malfunctioning of one of the two, to interrupt the treatment or to reset it to preset values.
This, however, implies the availability of supplying machines with two transducers, with the inconvenience that the cost of the extra device will heavily affect the overall cost of the machines, limiting their diffusion and the capacity of the therapeutic treatments.
Furthermore, the methodology used for coupling the two transducers, due to the natural deviation between them and to the instability of the anchorage between them, causes further and greater errors.